Method and apparatus for protecting a screw extruder producing strand-shaped explosives and propellants

ABSTRACT

A method and apparatus for protecting a mixing apparatus for producing strand-shaped explosives and propellants in a twin-shaft screw extruder, the housing of which is formed of housing parts connected to a clamping device acting under hydraulic pressure. In order to compensate for excessive pressure and to prevent abrupt opening of the mixing chamber, the torque developed at the screw shafts is continuously monitered and fed to a control and storage device together with temperature and pressure values measured at the end of the screw shaft in the material being processed. If one of the measure values exceeds a permissable limit, a signal is produced to change the operating condition of the screw extruder, particularly to stop and withdraw the extruder from the housing, to halt the drive motor of the extruder shafts and to open the extruder housing by relieving the clamping device.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for protecting ascrew extruder producing strand-shaped explosives and propellants.

The invention particularly relates to a twin shaft screw extruder whosehousing comprises a plurality of housing parts connected by clampingmeans.

DESCRIPTION OF PRIOR ART

DE-PS No. 2,825,567 discloses a method for the production of mixtures ofexplosives in a screw extruder whose housing is formed of severalhousing sections and in which various technical process parameters, suchas, among others, the torque delivered to the screw extruder, and thetemperature and pressure of the composition are transmitted to ameasuring station separate from the screw extruder and monitoredthereat. The measuring station serves as an operating station fornecessary intervention into the course of the process. Aside from this,there are no means disclosed for protecting the mixing process in thescrew extruder against the constant danger of an explosion.

A safety device for extruder housings for preventing impermissibleincreases in the pressure of a plastic melt in the extruder is disclosedin DE-PS No. 2,707,351, in which the housing is comprised of partsconnected to each other by relaxed pressure elements which retain thehousing parts when they are pressurized beyond their strength values.

This does not protect the mixing process itself or brace the housingparts in the operating condition.

Furthermore, the safety device in this patent is inapplicable to a screwextruder adapted for the production of strand-shaped explosives andpropellants, in view of the detonation wave which is suddenly propagatedin case of an explosion.

This is also true for the screw extruder for the production ofpyrotechnical compositions disclosed in DE-PS No. 2,642,153, in whichsafety of the screw extruder is effected by intended rupture of clampbolts at designated locations with subsequent swinging open of the screwhousing, which is divided into two halves.

Such safety devices provided with safety bolts of reduced strength willnot prevent the destruction of machine parts and the related endangeringof further equipment and operating personnel.

SUMMARY OF THE INVENTION

It is an object of the invention to avoid the above noted disadvantagesby providing a suitable protection for the mixing process and of thescrew extruder which, in case of danger, is immediately active tocompensate for excess pressure but which prevents an abrupt opening ofthe mixing chamber.

The above and further objects are achieved in accordance with theinvention by continuously measuring the torque at which the screw shaftsare driven and the pressure and temperature of the material in thehousing after mixing by the screw shafts, and comparing the measuredvalues of torque, temperature and pressure with respective predeterminedlimit values thereof. In the event any one of the measured valuesexceeds the respective limit value, the drive of the screw shafts of thescrew extruder is halted, the screw shafts are withdrawn from thehousing and the housing parts are unclamped by relieving hydraulicpressure acting thereon.

The hydraulic pressure is developed by a hydraulic clamping means whichpresses the housing parts of the housing against one another in clampedcondition via a counterpressure plate and distributor and retainerplates. The hydraulic clamping device includes a piston cylinder unithaving a cylinder, a piston in the cylinder, a piston rod secured to thepiston and to the retainer plate, whereas the cylinder is connected tothe pressure plate, the extruder screw having a longidutinal axis ofrotation and the cylinder, piston and piston rod being parallel to thelongitudinal axis.

As is known, the production of explosives and propellants in a screwextruder takes place at relatively high pressures and temperatures, sothat there is the constant danger of an autocatalytic reaction and ofthe material being processed catching fire.

A special feature of the process resides, on the one hand, in the factthat the mixing process, which is determined by means of essentialparameters, is not only continuously monitored but is also specificallyinfluenced by the elimination of any dangerous factors which occur. Suchdangerous factors arise as a result of exceeding the temperature orpressure of the composition, and the maximum permissible torque which isintroduced into the material being processed. If only a single one ofthese parameters is exceeded, the screw extruder is immediately shutdown and the extruder housing is simultaneously opened so that anyincreased gas pressure which develops rapidly in the case of adisturbance can immediately escape from the extruder housing. In case ofa disturbance, the mixing process is interrupted and the material beingprocessed in vented.

Furthermore, in the event of a sudden decomposition of the materialbeing processed with a subsequent explosion, the venting does not takeplace abruptly, but initially against the closing pressure of thehydraulically actuated clamping means. Upon the simultaneous exceedingof one of the monitored parameters, there takes place at the same time arelieving of the hydraulically actuated clamping means.

Reaction gases which are produced in case of a disturbance, i.e. uponexceeding the monitored parameters, are immediately discharged into theambient atmosphere even with a minute opening of the screw housing.

In the case of a detonation, the hydraulic circuit of the clamping meansacts as a buffer which prevents acceleration of parts of the mass of theapparatus from taking place.

If the drive device includes a hydraulic motor, the monitoring of thetorque thereof is made possible in a simple manner by including apressure gage in the hydraulic circuit. The control and storage devicesserve in this case for the monitoring both of this parameter and of thepressure of the composition and the temperature at the screw end, forthe purpose of changing the operating conditions, i.e. shutting down theextruder and opening the extruder housing for complete relief of theinternal pressure in the housing.

Furthermore, the method of the invention makes the opening of theextruder possible in simple manner by relieving the clamping means andmoving the housing parts away from one another to enable the completecleaning of all parts of the extruder. The construction of the apparatuspermits a sealed assembly of all housing parts. The closing pressureobtained in this respect by actuation of the piston of the hydraulicclamping means in the closing direction acts uniformly on all sealingsurfaces of the individual housing parts. Conversely, upon relieving theclosing pressure and with opposite action on the piston in the directionof opening, all housing parts can be easily separated from each other,so that the mixing chambers of the screw housing and the extruder screware both easily accessible for cleaning.

In a further development according to the invention, the separation ofthe housing parts from the extruder screw takes place automatically, sothat time-consuming removal of these housing parts, which is customarilydone by hand with the use of tools, is eliminated.

The retainer plate at one end of the mixing cavity can be opened forinspection purposes, without separation of the other housing parts,according to a further development in which a passage bore of the cavityretainer plate is easily accessible from the outside, so that areplacement of the cavity block is possible without the removal of anyfurther parts of the apparatus. This construction furthermore makesstepwise removal possible by first removing the cavity retainer platebefore loosening the housing parts.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING

The invention will be described in further detail below with referenceto an embodiment shown in the drawing, in which:

FIG. 1 is an elevation view of the screw extruder according to theinvention in operating manner.

FIG. 2 is a view of a portion of the screw extruder in opened condition.

FIG. 3 is an end view of the screw extruder in the direction towards itscavity retainer plate.

FIG. 4 is a portion of a section taken along line IV--IV in FIG. 3, withpartial opening of the screw extruder, i.e. with extracted cavityretainer plate.

FIG. 5 is a circuit diagram of the sequential controls for an electricdrive motor and the clamping means of the screw extruder.

FIG. 6 is a circuit diagram of the sequential controls for a hydraulicdrive motor and the clamping means of the screw extruder.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A twin shaft screw extruder 1 is shown in FIG. 1 which comprises twoscrews 2, 2' rotatably supported in a screw housing 3 comprised of aplurality of housing parts 4, 5 and 6. As will be described in greaterdetail below, the housing parts 4, 5 and 6 are tightly pressed againsteach other. The screw extruder 1 is driven by a drive means 7 whichincludes a drive motor 8 and a transmission 9. The drive motor 8 can bean electric drive motor 81 of explosion-proof type or a hydraulic motor82. The drive motor 8 and the transmission 9 are connected to each otherby a mechanical coupling 10.

The screws 2, 2' are connected to corresponding drive shafts 11 byrespective couplings 12. The mechanical energy introduced through thedrive means 7 is introduced into the material being processed over theentire length of the screw housing by means of the double screws 2, 2',with the formation of shearing forces, the mixing effect obtained inthis connection serving for the preparation and conditioning of astrand-shaped final product.

In the extruder, solids and solvents, such as, for example, mono- andpolybase propellant powder, are thoroughly mixed to form a homogeneoussubstance.

The addition of the solid and liquid components into the screw housing 3takes place through a feed hopper 13. The material being processed,which is continuously worked by means of the screws 2, 2', is dischargedthrough nozzle openings 14 and 15 in a cavity retainer plate 16, asstrands which are cut into a finished product of predetermined length bycutting devices 17 and 18.

The entire treatment process takes place with sealed closure of thehousing parts 4, 5, 6, which are clamped together in a manner describedbelow, and with the cavity retainer plate 16 pressed against adistributor plate 30 and, together with the latter, against the endmostscrew housing part 6. A counterpressure plate 19 resists the clampingforces and is connected in releasable manner to the screw housing 3 orthe housing part 4 and also resists, via tie rods 20, 21, backpressureforces of the screws 2, 2' by means of an abutment, not shown in detail.

In order to establish a separable clamping effect, the cavity retainerplate 16 and the counterpressure plate 19 are connected by clampingmeans comprised of piston-cylinder units 22, 23. Cylinders 24, 25 ofunits 22, 23 are fastened to the counterpressure plate 19 andcorresponding piston rods 26, 27 of units 23, 23 are fastened to thecavity retainer plate 16. Pressure is applied in the piston-cylinderunits 22 and 23 in the direction of the closing of the housing parts 4,5 and 6 by the introduction of pressure fluid via hydraulic connections28 and 29 to produce a tight clamping of the housing parts 4, 5 and 6against one another and a clamping of the retainer plate 16 against thedistributor plate 30.

In the operating condition of the screw extruder 1, therefore, allhousing parts forming its mixing and extrusion chambers are permanentlyclamped in tight manner with respect to each other under hydrauliccompressive force. The action of the pressure on the piston-cylinderunits 22, 23 in the direction of closing with clamping of the retainerplate 16 and of the housing parts 4, 5 and 6 takes place with a pressureof about 300 bar of hydraulic liquid. In order to prevent the opening ofthe screw extruder 1 under normal operating conditions, the piston 80 ofeach piston-cylinder unit 22, 23 is acted on by an adjustable pressure,so that its pressing force at any time is about 10% above thecorresponding internal extruder pressure, which is dependent on thematerial being processed. The internal extruder pressure can be up toabout 300 bar. The pressure in each unit 22, 23 is manually adjustableby a pressure relief valve 88. All of the piston-cylinder units 22, 23are connected hydraulically in customary manner to a hydraulic liquidpump 67 such that absolutely uniform operation of the piston rods 26, 27is obtained.

In the case of danger, i.e. upon suddenly exceeding the permissiblepressure of the composition in the screw extruder 1, the screw housing 3opens for immediate pressure relief at one of the sealing surfaces ofthe housing 4, 5, 6 which is closest to the source of danger.

In order to make it possible to open the housing parts 4, 5, 6 and theretainer plate 16 as easily as possible, these parts are mounted fordisplacement relative to the machine frame 36, in each case on aplurality of ball bushings 32, 33, 34 and 35.

The arrangement of the ball bushings 32, 33, 34 and 35 is such, as shownin particular in FIGS. 3 and 4, that they are securely connected, on theone hand, by means of a fastening plate 37 to the retainer plate 16 or,in each case, by means of additional fastening plates 38, 39 and 40 tothe housing parts 4, 5 and 6. The ball bushings 32, 33, 34 and 35 areguided on sliding pistons 50, 51 of cylindrical cross section which arefirmly connected to the machine frame 36 by fastening elements 52, 53.

The smooth mobility of this arrangement makes a "breathing" of theextruder housing possible, so that upon an explosively increasing excesspressure in the material being processed, a rapid opening of the housingparts 4, 5 and 6, and of the retainer plate 16, which are clampedagainst each other by the piston-cylinders serving as a hydraulicbuffer, is assured.

The hydraulic clamping means (piston-cylinder units 22, 23) thus serves,mainly, to protect the screw extruder 1 and prevent the destruction ofits components.

As can be seen in FIGS. 5 and 6, the screw extruder 1 is furtherconstructed for this purpose with sequential controls, which result inprotection not only in the case of a detonation of the material beingprocessed, but also protection of the extruder in the case of danger dueto excess pressure, excess temperature and increased torque in the screwextruder 1.

FIG. 5 shows a sequential controller for a drive of the screw extruder 1by an electric motor whereas FIG. 6 shows such a controller for ahydraulic drive of the screw extruder 1. In both circuit diagrams, thehydraulic circuit for the clamping means (piston-cylinder units 22, 23)is essentially the same.

The drive of the screw extruder 1 takes place, in accordance with FIG.5, by means of an explosion-proof electric motor 81 which can beconnected to and disconnected from an electrical line 54 including arelay switch 55. The consumption of electrical current by the electricmotor 81 is continuously monitored by an ammeter 44 and fed to acontrolling and storage device 41 where it is compared with a storeddesired value for the current.

The temperature and pressure values are respectively determined by atemperature sensor 83 and a pressure sensor 84 near the discharge end ofthe screw shaft and are fed to the control and storage device 41 andcompared thereat with corresponding stored desired values. For thispurpose, sensors 83 and 84 are connected to the control and storagedevice 41 by lines 85 and 86. After a positive comparison with thecorresponding desired value in the control and storage device 41, asignal is derived from each of the actual values determined, the pulseof said signal acting on the relay switch 55 and on a 4/3-way valve 42.The 4/3-way valve 42 controls the piston-cylinder units 22, 23 and canbe switched by means of solenoid valves a or b. If any one of the valuesof the torque, pressure or temperature in the screw extruder 1 exceedsthe desired, comparative value, actuation of the relay switch 55 via acontrol line 43 takes place and the drive motor 81 is halted. Thesolenoid valve b is simultaneously energized via a further control line56, so that the piston-cylinder units 22, 23 are relieved and slowlyopened. This brings about an opening of the extruder housing 3 a byseparation movement of the housing parts 4, 5 and 6 and the retainerplate 16. The slow outward movement of the piston rods 26 and 27 resultsfrom the forced displacement of the pressure medium present in thepiston-cylinder units 22, 23. This change in the pressure medium is alsothe controlling cause for the fact that, upon an explosion in the screwextruder 1, its components are not flung off, but, rather, make possiblea braked opening movement against the pressure medium, which acts as abuffer.

In the switch position shown for the 4/3-way valve 42, thepiston-cylinder units 22, 23 are without hydraulic pressure, in extendedcondition in a position of rest. As shown in FIG. 2, all housing parts4, 5 and 6 have been retracted from the two screws 2, 2' so that accessto the screws 2, 2' and to the housing parts 4, 5, 6 for cleaning ismade possible.

A drag rod 47 serves for the partial opening of the screw extruder 1merely by moving the retainer plate 16 outward for the cleaning thereof.

As shown in FIG. 1, the drag rod 47 is fastened by a flange 87 to theretainer plate 16, is guided in a guide part 48, and has a driver cam 49at a distance l from the housing part 5. The guide part 48 is fastenedto the housing part 4 in the region thereof directly adjoining thehousing part 5. For moving the retainer plate 1l outward, a stop device57 is arranged on the machine frame 36, as shown in FIG. 4, forpreventing separation movement of the fastening plates 38, 39, and 40and of the housing parts 4, 5 and 6 connected to them. Upon actuation ofthe switch device 45, the magnet b of the 4/3-way valve is excited viathe control line 59, and the magnet c of the 4/2-way valve is excitedvia the control line 60 according to FIG. 5 and the retainer plate 16 ismoved outward by means of the piston-cylinder units 22, 23, without thehousing parts 4, 5 and 6. The stop device 57 consists of apiston-cylinder unit 61 the piston 63 of which comes to rest against thefastening plate 40 of the housing part 6 when acted on by pressureagainst the force of a compression spring 62. In the operating conditionof the screw extruder 1, i.e. with the screw housing 3 closed, thepiston 63 remains in retracted position, so that the housing parts 4, 5and 6 are free to move.

The clamping together of the housing parts 4, 5 and 6, and of theretainer plate 16, which is controlling for the operating condition ofthe extruder 1, takes place by actuating the switch device 45 andexciting the magnet a of the 4/3-way valve 42 via the control line 46.The piston-cylinder units 22 and 23 are in this way brought into theirclamping position.

A relaxation of this clamping condition takes place, as alreadydescribed, in the event of danger, by producing a signal by the controland storage device 41 in the control lines 43 and 56.

A relaxation of the clamping condition can take place, as has alsoalready been described, by hand through the switch device 45. In orderto assure the clamping action of the piston-cylinder units, 22, 23, forinstance upon the occurrence of a leak in the hydraulic circuit, thelatter is connected to a pressure accumulator 65. The hydraulic circuitfor actuating the piston-cylinder units 22, 23 consists furthermore of afeed pump 67 driven by electric motor 66, and in communication viahydraulic lines 68 and 69 with the 4/3-way valve 42 and the 4/2-wayvalve 58 respectively, while the accumulator 65 is connected via abypass 70 to the feed pump 67. The outputs of the 4/3-way valve 42 areconnected by further hydraulic lines 71 and 72 to the connections 28 and29 of the piston-cylinder units 22, 23.

If the drive means 7 of the screw extruder includes the hydraulic motor82, then the latter, as shown in FIG. 6, is fed by means of anadjustable hydraulic pump 73 via a hydraulic line 74. The hydraulic line74 is in this case connected to a pressure-measuring device 75, whichcontinuously determines the pressure of the pressure fluid feeding thehydraulic motor 82 and transmits it as a measured value via an electricline 76 to the control and storage device 41. In the latter, there iseffected, as described above with reference to FIG. 5, a comparison ofthe actual value with a desired value stored therein and when the actualvalue exceeds the desired value, an electrical signal is produced inline 79 which is fed to the relay switch 77 for halting the feed-pumpmotor 78, said signal acting at the same time on the 4/3-way valve 42via the line 56 for opening the housing parts 4, 5 and 6 and thereatainer plate 16.

In accordance with the above, an actuating of the screw extruder 1 isobtained for protecting the mixing process in the operating condition,in which the screw housing 3 with its housing parts 4, 5 and 6 opensautomatically, in the case of a detonation, against the buffer action ofthe hydraulic medium in the piston-cylinder units 22, 23 and thehydraulic circuit connected to the latter. This opening movement isaccompanied by the immediate halting of the screw extruder 1.

Due to the inertia of the hydraulic liquid, the opening does not takeplace abruptly, so that the components of the screw extruder areprotected against destruction.

A controlled actuation of the screw extruder 1 furthermore takes placeupon an increase in the temperature and/or pressure in the materialbeing processed, and in case excessive drive torque.

In this case also, the mixing process is made substantially safe, andthe screw extruder 1 is protected against destruction.

The possibility of manually opening the screw extruder by the switchdevice 45 also serves to protect the mixing process and the screwextruder. The switch device is located outside the housing but in visualcontact within the room in which the screw extruder 1 is located. Incase of any irregularities, the housing parts 4, 5 and 6, as well as thescrews 2, 2' can rapidly be completely cleaned after a waiting periodand after the opening of the screw extruder 1, in order to assure theproper course of the subsequent mixing processes.

Although the invention has been described in relation to specificembodiments thereof, it will become apparent to those skilled in the artthat numerous modifications and variations can be made within the scopeand spirit of the invention as defined in the attached claims.

What is claimed is:
 1. A safety method for protecting a mixing apparatusin which strand-shaped explosives and propellants are produced by ascrew extruder, said method comprisingforming a housing for a screwextruder of a mixing apparatus for the production of strand-shapedexplosives and propellants of a plurality of separable housing parts,clamping the housing parts together under hydraulic pressure, drivingscrew shafts of the screw extruder in the housing with a determinedtorque to mix the material being processed, continuously measuring thetorque at which the screw shafts are driven, measuring the temperatureof the material in the housing after mixing by the screw shafts,mesuring the pressure of the material in the housing after mixing by thescrew shafts, respectively comparing the measured values of torque,temperature and pressure with predetermined limit values thereof, and inthe event any one of the measured values exceeds the respective limitvalue, halting the drive of the screw shafts of the screw extruder,separating the screw shafts from the housing, and unclamping the housingparts by relieving the hydraulic pressure acting thereon.
 2. A method asclaimed in claim 1 wherein said screw shafts have ends at which thematerial is discharged from the housing, said pressure and temperatureof the material being measured in the vicinity of the ends of the screwshafts.
 3. A method as claimed in claim 1 wherein said housing parts areunclamped under the control of a hydraulic circuit in which iseffectedpumping hydraulic fluid via a pressure accumulator to a switchvalve, controlling said switch valve, in accordance with detection thatone of the measured values exceeds its respective limit value, torelieve the hydraulic pressure acting on the housing parts, andactivating a relay to interrupt power delivery to the drive of the screwshafts.
 4. A method as claimed in claim 1 wherein the drive of the screwshafts is effected by a hydraulic motor, the measurement of the torquewhich acts to mix the material being effected by measuring the hydraulicpressure of said hydraulic motor.
 5. A method as claimed in claim 1comprising manually controlling unclamping of the housing parts.
 6. Amethod as claimed in claim 5 wherein the manual control for unclampingthe housing parts is effected from outside the housing.
 7. A mixingapparatus including protective safety means in which strand-shapedexplosives and propellants are produced, said apparatus comprising ahousing including a plurality of separable housing parts,a screwextruder in said housing for mixing material being processed to producestrand-shaped explosives and propellants, means for clamping saidhousing parts together under hydraulic pressure, drive means for drivingsaid screw extruder in the housing with a determined torque to mix thematerial being processed, means for continuously measuring the torque atwhich said screw extruder is driven, means for measuring the temperatureof the material in the housing after mixing by the screw extruder, meansfor measuring the pressure of the material in the housing after mixingby the screw extruder, control means for respectively comparing themeasured values of torque, temperature and pressure with predeterminedlimit values thereof, means for halting the screw extruder, means forwithdrawing the screw extruder from the housing, means for unclampingthe housing parts by relieving the hydraulic pressure acting thereon,and means for activating the means for halting the screw extruder, themeans for withdrawing the extruder from the housing and the means forunclamping the housing parts when one of the measured values exceeds itsrespective limit value.
 8. Apparatus as claimed in claim 7 wherein saidscrew extruder includes screw shafts having ends at which the materialis discharged from the housing, said means for measuring pressure andsaid means for measuring temperature of the material comprisingrespective sensors disposed in the vicinity of the ends of the screwshafts.
 9. Apparatus as claimed in claim 7 wherein said means forclamping said housing parts together comprises a hydraulic circuitincluding a hydraulic pump,a pressure accumulator coupled to said pump,a switch valve connected to said pump and to said accumulator forcontrolling flowing hydraulic fluid to said clamping means, means foroperating said switch valve upon detection that one of the measuredvalues exceeds its respective limit value to relieve the hydraulicpressure acting on the housing parts, and a relay connected to saidcontrol means and to said drive means to interrupt power delivery to thedrive means fothe screw shafts when one of the measured values exceedsits respective limit value.
 10. Apparatus as claimed in claim 7 whereinsaid drive means for the screw extruder comprises a hydraulic motor,said means for measuring the torque comprising a sensor measuring thehydraulic pressure of said hydraulic motor.
 11. Apparatus as claimed inclaim 7 comprising manually operated switch means for controlling themeans for unclamping the housing parts.
 12. A screw extruder apparatusfor producing strand-shaped explosive and propellant materials underrelatively safe conditions, comprisinga housing including a plurality ofadjacent housing parts arranged end to end one after the other andmoveable towards and away from one another, a distributor plate adjacentto an endmost one of the housing parts, a retainer plate adjacent tosaid distributor plate at an outlet end of the housing, acounterpressure plate adjacent to an opposite endmost one of the housingparts, an extruder screw mounted in said housing, drive means forrotating said extruder screw, and hydraulic clamping means for pressingthe housing parts against one another in clamped relation via saidcounterpressure plate and said distributor and retainer plates, saidhydraulic clamping means including a piston-cylinder unit comprising acylinder, a piston in said cylinder and a piston rod secured to saidpiston, said piston rod being secured to said retainer plate, saidcylinder being connected to said counterpressure plate, said extruderscrew having a longitudinal axis of rotation, said cylinder, piston andpiston rod being parallel to said longitudinal axis.
 13. A screwextruder as claimed in claim 12 wherein said extruder screw is removablefrom said housing by relative movement thereof parallel to saidlongitudinal axis.
 14. A screw extruder as claimed in claim 12comprising a guide secured to the opposite endmost ones of the housingparts, a drag rod extending parallel to said longitudinal axis andsecured to said retainer plate end displaceably supported in said guide,and a driver on said drag rod spaced from said guide when the housingparts are clamped together.
 15. A screw extruder as claimed in claim 14comprising a fixedly supported stop means for selectively blockingmovement of said housing parts from said clamped condition.
 16. A screwextruder as claimed in claim 15 wherein said stop means includes ahydraulic piston-cylinder unit having a spring-loaded piston mounted ina cylinder.
 17. A screw extruder as claimed in claim 14 comprising amachine frame, and ball bushings supporting said housing parts forslidable movement on said machine frame.
 18. A screw extruder as claimedin claim 12 wherein said hydraulic clamping means comprises four of saidpiston-cylinder units spaced equally from said longitudinal axis and anadjustable pressure relief valve acting on said piston-cylinder units.19. A screw extruder as claimed in claim 12 comprising a temperaturesensor for measuring the temperature of the material in the housing, anda pressure sensor for measuring the pressure of the material in thehousing, said distributor plate having openings in which saidtemperature sensor and pressure sensors are received.